Radiation-Sensitive Thin Film Dosimeter Based on Polyvinyl Alcohol (PVA)/Hafnium Dioxide (HfO2)/Silver Nitrate (AgNO3) Composite: Colorimetric Characterization and Dose-Response Analysis for Low-Dose Gamma-Ray Applications.

The development of sensitive, low-cost, and visually readable dosimeters for low gamma-ray exposures is important for occupational and environmental radiation monitoring and for other low-dose applications. This work investigates a colorimetric and optical thin-film dosimeter based on polyvinyl alcohol (PVA) containing silver nitrate (AgNO3) and hafnium oxide (HfO2). The film was fabricated using a solution-casting technique. The dosimetric response was evaluated over an absorbed-dose range of 22.2-65.2 mGy using diffuse reflectance spectroscopy, Kubelka-Munk (K/S) analysis, CIELAB colorimetry, CMYK image-based analysis, and X-ray diffraction (XRD). Irradiation produced a dose-dependent decrease in visible reflectance and a corresponding increase in optical absorption. The K/S response increased with dose, while CIELAB analysis showed a systematic decrease in lightness and an increase in total color difference (ΔEab∗), reaching approximately 25 at 65.2 mGy. Linear regression of ΔEab∗ over 0-65.2 mGy gave y = 0.399x - 1.0029 with R2 = 0.9845. CMYK analysis also showed a clear dose response, with the yellow channel (ΔY) exhibiting the largest relative change among the chromatic channels. XRD identified monoclinic HfO2 as the dominant crystalline filler phase and showed dose-associated changes in peak intensity, peak position, and the relative prominence of the broad PVA-related feature. At the highest XRD dose, several HfO2 reflections weakened while the broad contribution near 2θ ≈ 19.9-20° became more prominent. These changes are interpreted as dose-dependent structural modification and partial loss of resolved crystalline order rather than definitive evidence of a newly formed crystalline phase. A surface morphology and microstructure analysis was performed on control and γ-ray-irradiated PVA/HfO2/AgNO3 nanocomposite films using scanning electron microscopy (SEM-EDX). The morphological transition to fibrous, tree trunk-like structures seen by SEM is well correlated with the dose-dependent change in composition to higher surface Ag content, supporting the idea that radiation-induced Ag nanoparticle nucleation and growth is the primary degradation mechanism in the irradiated films. The combined optical and colorimetric results demonstrate a measurable response of the PVA/HfO2/AgNO3 formulation in the investigated low-mGy gamma-ray range.